Refining steel



Patented Feb. 23, 1954 UNITED.

REFINING STEEL Camille Solsson, Rodange, Luxembourg No Drawing.

Application July 17, 1951,

Serial No. 237,290

Claims priority, application Luxembourg October 7, 1950 3 Claims. 1

The quality of steel is largely determined by its method of manufacture. Thus ordinary steels made on a large scale in large metallurgical works are distinguishedfrom refined steels obtained by more laborious processes but ensuring a much more complete deoxidation, therefore greater purity.

It is generally agreed that a high quality steel should contain less than 0.025% of phosphorus and of sulphur. Of these two elements it is above all the sulphur content which is believed to demand most attention, because the latter and oxygen'are so to speak two inseparable com panions. If one goes, the other also goes. In

other words, a steel of low sulphur content is usually well deoxidized, and therefore pure.

Small variations in phosphorus content appear to us to be of less importance, especially in the case of killed steel, where the harmful effects of phosphorus segregation are much reduced or no longer exist. According to the present opinion,

the quality improves considerably, above all when the sulphur content falls below 0.015%.

The main unfavourable characteristic of steel produced according to the Thomas process consists in the fact that at the end of the dephosphorizing period, when oxidation is at its maximum, the operation carried out in the converter is, practically finished. Of course, deoxidation can be carried out but there is no longer available the source of heat necessary for continuing the steel refining, that is to say for continuing to heat the bath and to permit the inclusions-formed by the products of deoxidation to escape in gaseous form or to segregate in the refining slag.

This absence from the purifying or refining stage is the main reason, and probably the sole reason, for the fact that steel produced according to the Thomas process is reputed to contain more inclusions than steel manufactured according to the Martin process or in the electric furnace.

If it is desired to obtain a cleaner metal, it is therefore necessary to use a duplex process by passing it through a Martin or electric furnace for refining, which considerably increases the cost. Moreover, in most cases the existing plant does not permit this supplementary operation.

Tests have been carried out in the application of the processes generally known as double slag processes, which consist in removing the greater part of the first slag, then adding lime and a supplier of heat such as aluminium or silicon, and blowing until the second slag melts. This slag.

which is more basic and has a lower concentration of phosphoric acid, undoubtedly permits the production of 2. Thomas steel improved from the point of View of the content of phosphorus and sulphur. The steel works used for these tests were particularly suitable, because they allowed the steel to be transferred into a second converter. As it appeared that the slag removal was always insufficient, it was decided to make use of a new converter which was not impregnated with phosphorus, inorder to carry out the second refining treatment therein. A trial run was carried out for mild steel, ,the additions being made accordingly. The charge for form-,

ing the second slag was the same as for the previous tests:

Lime 2-50 CaFz ..l. 50 FeSi 30 The results of analysis of this steel were unexpected:

P Mn 0 s Normal blast 0.020 0. 0. 040 0. 048 After refilling 0. 033 0. 120 0. 120 0. 011 In the ladle 0. 043 0. 750 0. 0. 01a

The solution of the problem was soon found.

As the new converter had been heated with coke before serving for the refining of the test pour-j ing, the lining had become impregnated with carbon, and in this way the casting had been completed in the reducing phase. Killed steel was cast. The yield from the added manganese was 100%, and desulphurisation I was very thorough.

The slag had the following composition:

Slog CaO Fe lVlIi P205 A1205 S 3 absolutely white. The yield from manganese, whether added in the form of ferro-manganese or in the form of ore, is 100%. The values of the transverse resiliences come substantially near to those of the longitudinal resiliences. The new steel hardly ages at all.

The invention accordingly consists in a process of refining steel which consists in adding aluminium metal to the molten steel in a converter. The Vigorous stirring and the heat given 011 by the oxidation of the aluminium make it possible to carry out in the converter in record time, a refining more thorough than in other metallurgical furnaces.

In order better to illustrate the process, here are the results of casting No. 74,009.

The following materials were charged into the converter serving for the refining:

100 kg. metallic aluminium.

40 kg. manganese ore (40% Mn) 20 kg. ferro-silicon 75%.

250 kg. pulverised lime.

50' kg. calcium fluoride.

On top of the mixture about 12 metric tons of molten Thomas steel which had been dephosphorized according to the normal process were poured, the analysis of the steel being as follows:

P 0.034 Mn 0.140 c 0.030 s 0.035

After two periods of light blowing, lasting 13 and 8 seconds respectively, the whole refining operation was finished.

Analysis of the final slag:

Test performed by Societe des Hauts-Fourneaux de la. Chiers (of'the city of Chiers France).

2 Test performed by the Company Rodange (of Rodauge, Luxembourg).

Technological tests gave as resiliences the following mean values (CMA method) for billets of 50 mm. square:

Commission Mixte des Aciers (Fabrimetal This test consists in the comparative resistance to s o'cks before and after artificial aging of the metal bv hammering followed by 1E hefltil2%.l This test can be ected by traction or compression. e numbers indicated in ligmJcm. refer to the capacity to resist shock after hammering by traction and the remanent extention of themetal of 5 or Crude rolling state:

Longitudinal 19.3 Transverse 17.9 Drawn 5%, longitudinal 17.5 Drawn 10%, longitudinal 17.2 Drawn 5% and aged, longitudinal 17.7 Drawn 10% and aged, longitudinal 15.9

The results obtained are confirmed by numerous control analyses, as well as by hundreds of technological tests. The fact that the transverse resiliences and the resiliences after cold-drawing and artificial ageing are 5 to 10 times greater than those for-an ordinary Thomas steel of the same composition, is even more convincing than the other figures.

I claim:

1. The method of rapidly refining ordinary steel in a converter for transforming the same into a high quality steel of low sulfur content which comprises heating the molten steel in the converter by addition thereto of metallic aluminum and violently agitating the molten steel with a blast of air and terminating the blowing while the steel is in the reducin phase.

2. The method of rapidly refining ordinary steel in a converter for transforming the same into a high quality steel of low sulfur content which comprises heating the molten steel in a basic converter by addition thereto of metallic aluminum and violently agitating the molten steel with a blast of air, the oxidizing blast applied being terminated while the steel is in the reducing phase whereby the refining is efiected in the presence of a basic slag in a reducing phase to produce a mild steel.

3. The method of refining steel as defined in claim 1, wherein the ordinary molten steel has been dephosphorized and is added to the converter containing a basic slag and aluminum metal, the oxidizing blast being terminated while the steel is in the reducing phase whereby the refining is efiected' in a reducing phase in the presence of a basic slag to produce a mild steel.

CAMILLE SOISSQN.

References Cited in the file of this patent. UNITED STATES PATENTS Number Name Date 2,207,109 Perrin July 9, 1940 2,288,830 Perrin July 7, 1942 FOREIGN PATENTS Number Country Date 861,427 France Feb. 8, 1941 

1. THE METHOD OF RAPIDLY REFINING ORDINARY STEEL IN A CONVERTER FOR TRANSFORMING THE SAME INTO A HIGH QUALITY STEEL OF LOW SULFUR CONTENT WHICH COMPRISES HEATING THE MOLTEN STEEL IN THE CONVERTER BY ADDITION THERETO OF METALLIC ALUMINUM AND VIOLENTLY AGITATING THE MOLTEN STEEL WITH A BLAST OF AIR AND TERMINATING THE BLOWING WHILE THE STEEL IS IN THE REDUCING PHASE. 